The growth, morphogenesis, and cytodifferentiation of embryonic and postnatal rat lung tissue is a well-characterized process at the level of the light and electron microscope. The course of lung development, however is a complex process involving the differentiation of a wide variety of cell types from progenitor cells in the mesenchyme and endothelium. The goal of the work proposed herein is to investigate the hypothesis that cell surface saccharide structures are important to the initial recognition, aggregation, adhesion, and organization of these diverse cell types with lung tissue. Our approach is to study the surface saccharides of alveolar Type 1 and Type 2 cells throughout rat lung development by staining glutaraldehyde-fixed lung tissue with ferritin-conjugated lectins and detecting the bound lectins using an electron microscope. By using a series of ferritin-conjugated lectins with varying saccharide specificity, we will be able to determine whether there are any developmentally associated changes in cell surface saccharide structures. The cell surface saccharides that are unique to a given cell type or time of development will be isolated from (35S)-methionine-labeled, detergent-solubilized lung extracts by lectin affinity chromatography and characterized by sodium dodecylsulfate polyacrylamide gel electrophoresis. In addition to elucidating the role of cell surface saccharide structure in cell differentiation and development, a knowledge of the lectin specificity of lung cell surfaces will provide a simple and rapid method for the isolation and characterization of lung cells in vitro and may suggest methods for assessing prenatal lung maturity prior to the apearance of lung surfactant.